Abstract:

Disclosed herein is an optical article including a multilayer optical film
of alternating layers of first and second optical layers, wherein the
first and second optical layers have refractive indices along at least
one axis that differ by at least 0.04; and a protective layer disposed on
an outer surface of the multilayer optical film, the protective layer
having a thickness of less than about 0.5 um and including crosslinked
hydroxylated polymer. The optical article may further include a
microstructured layer disposed on an outer surface of the multilayer
optical film opposite the protective layer. Also disclosed herein are a
method of making the optical article and a display device including the
optical article.

Claims:

1. An optical article comprising:a multilayer optical film comprising
alternating layers of first and second optical layers, wherein the first
and second optical layers have refractive indices along at least one axis
that differ by at least 0.04; anda protective layer disposed on an outer
surface of the multilayer optical film, the protective layer having a
thickness of less than about 0.5 um and comprising a crosslinked
hydroxylated polymer, the crosslinked hydroxylated polymer comprising
poly(vinyl alcohol) or a vinyl alcohol copolymer.

2. The optical article of claim 1, the protective layer having a thickness
of less than about 0.3 um.

3. The optical article of claim 1, the protective layer having a thickness
of less than about 0.1 um.

4. The optical article of claim 1, wherein the crosslinked hydroxylated
polymer is derived from poly(vinyl alcohol) having a degree of hydrolysis
of from 88 to 98%.

5. The optical article of claim 1, wherein the crosslinked hydroxylated
polymer is derived from poly(vinyl alcohol) having a degree of hydrolysis
of from 88 to 95%.

6. The optical article of claim 1, wherein the crosslinked hydroxylated
polymer is derived from poly(vinyl alcohol) having a 4% solution
viscosity of from 4 to 56 cP.

7. The optical article of claim 1, wherein the crosslinked hydroxylated
polymer is derived from poly(vinyl alcohol) having a 4% solution
viscosity of from 18 to 40 cP.

8. The optical article of claim 1, wherein the crosslinked hydroxylated
polymer further comprises a crosslinking agent, the crosslinking agent
may comprise glutaraldehyde, an epoxy, an isocyanate, a zirconium
carboxylate complex, an epichlorohydrin/amine adduct, a
melamine/formaldehyde resin, a poly(carbodiimide), or a combination
thereof.

9. The optical article of claim 1, wherein the crosslinked hydroxylated
polymer is derived from poly(vinyl alcohol) and a crosslinking agent in a
ratio of from about 20:1 to about 5:1.

10. The optical article of claim 1, wherein the crosslinked hydroxylated
polymer is derived from poly(vinyl alcohol) and a crosslinking agent in a
ratio of from about 15:1 to about 7:1.

11. The optical article of claim 1, wherein the crosslinked hydroxylated
polymer is derived from poly(vinyl alcohol) and a crosslinking agent in a
ratio of from about 12:1 to about 9:1.

12. The optical article of claim 1, wherein the multilayer optical film
comprises a reflective film, a polarizer film, a reflective polarizer
film, a diffuse blend reflective polarizer film, a diffuser film, a
brightness enhancing film, a turning film, a mirror film, or a
combination thereof.

13. The optical article of claim 1, further comprising a microstructured
layer disposed on an outer surface of the multilayer optical film
opposite the protective layer, wherein the microstructured layer
comprises a structured surface having a plurality of microstructures, and
the structured surface comprises an outer surface of the optical article.

14. A method of making an optical article, comprising:providing a
multilayer optical film comprising alternating layers of first and second
optical layers, wherein the first and second optical layers have
refractive indices along at least one axis that differ by at least
0.04;coating a protective layer composition on the multilayer optical
film, the protective layer composition comprising hydroxylated polymer
and a crosslinking agent; anddrying the protective layer composition
thereby forming a protective layer having a thickness of less than about
0.5 um.

15. The method of claim 14, the protective layer having a thickness of
less than about 0.3 um.

16. The method of claim 14, the protective layer having a thickness of
less than about 0.1 um.

17. The method of claim 14, wherein the hydroxylated polymer comprises
poly(vinyl alcohol) having a degree of hydrolysis of from 88 to 98% and a
4% solution viscosity of from 4 to 56 cP.

18. The method of claim 14, wherein the protective layer composition
comprises a crosslinking agent, the crosslinking agent may comprise
glutaraldehyde, an epoxy, an isocyanate, a zirconium carboxylate complex,
an epichlorohydrin/amine adduct, a melamine/formaldehyde resin, a
poly(carbodiimide), or a combination thereof.

19. The method of claim 14, wherein the protective layer composition
comprises poly(vinyl alcohol) and a crosslinking agent in a ratio of from
about 20:1 to about 5:1.

20. The method of claim 14, wherein the multilayer optical film comprises
a reflective film, a polarizer film, a reflective polarizer film, a
diffuse blend reflective polarizer film, a diffuser film, a brightness
enhancing film, a turning film, a mirror film, or a combination thereof.

21. The method of claim 14, further comprising forming a microstructured
layer disposed on an outer surface of the multilayer optical film
opposite the protective layer, wherein the microstructured layer
comprises a structured surface having a plurality of microstructures, and
the structured surface comprises an outer surface of the optical article.

22. A display device comprising:a display panel;a light source; andan
optical article disposed between the display panel and the light source,
the optical article comprising:a multilayer optical film comprising
alternating layers of first and second optical layers, wherein the first
and second optical layers have refractive indices along at least one axis
that differ by at least 0.04; anda protective layer disposed on an outer
surface of the multilayer optical film, the protective layer having a
thickness of less than about 0.5 um and comprising crosslinked
hydroxylated polymer.

23. The display device of claim 22, wherein the optical article further
comprises a microstructured layer disposed on an outer surface of the
multilayer optical film opposite the protective layer, wherein the
microstructured layer comprises a structured surface having a plurality
of microstructures, and the structured surface comprises an outer surface
of the optical article.

24. A method of making an optical article, comprising:providing a
substrate comprising alternating layers of first and second optical
layers;coating a protective layer composition on the multilayer optical
film, the protective layer composition comprising hydroxylated polymer
and a crosslinking agent;drying the protective layer composition thereby
forming a protective layer having a thickness of less than about 0.5 um;
andstretching the coated substrate in at least one direction, whereby the
first and second optical layers have refractive indices along at least
one axis that differ by at least 0.04.

Description:

[0002]Many liquid crystal displays incorporate one or more types of
brightness enhancement (BEF) films to increase brightness and reduce
power consumption. One type of BEF film is a prismatic film comprising a
polymeric substrate bearing a layer of prism structures that act to
channel light into the field of view that would ordinarily be scattered
out to higher viewing angles. The prisms are applied by coating a
UV-curable acrylic resin on the polymer substrate followed by curing
against a microstructured roll. Another type of BEF film is a multilayer
optical film, typically a reflective polarizer, comprising alternating
layers of two different polymeric materials that have been extruded
together and subsequently stretched. Liquid crystal displays may
incorporate both types of BEF films in a configuration in which the prism
structures of a prismatic film are adjacent a multilayer optical film.
The prism pattern can "imprint" into the multilayer film. Prismatic films
in which the polymeric substrate is a multilayer optical film are also
known. When this type of BEF film is wound up in roll form, the prism
pattern can undesirably imprint into the multilayer optical film. In both
cases, imprinted prism structures can cause haze and disrupt optical
performance.

SUMMARY

[0003]In one aspect, disclosed herein is an optical article comprising: a
multilayer optical film comprising alternating layers of first and second
optical layers, wherein the first and second optical layers have
refractive indices along at least one axis that differ by at least 0.04;
and a protective layer disposed on an outer surface of the multilayer
optical film, the protective layer having a thickness of less than about
0.5 um and comprising crosslinked hydroxylated polymer. The multilayer
optical film may comprise a reflective film, a polarizer film, a
reflective polarizer film, a diffuse blend reflective polarizer film, a
diffuser film, a brightness enhancing film, a turning film, a mirror
film, or a combination thereof. The optical article may further comprise
a microstructured layer disposed on an outer surface of the multilayer
optical film opposite the protective layer, wherein the microstructured
layer comprises a structured surface having a plurality of
microstructures, and the structured surface comprises an outer surface of
the optical article.

[0004]In another aspect, also disclosed herein is a method of making the
optical article, comprising: providing a multilayer optical film
comprising alternating layers of first and second optical layers, wherein
the first and second optical layers have refractive indices along at
least one axis that differ by at least 0.04; coating a protective layer
composition on the multilayer optical film, the protective layer
composition comprising hydroxylated polymer and a crosslinking agent; and
drying the protective layer composition thereby forming a protective
layer having a thickness of less than about 0.5 um.

[0005]In another aspect, also disclosed herein is a display device
comprising: a display panel; a light source; and an optical article
disposed between the display panel and the light source, the optical
article comprising: a multilayer optical film comprising alternating
layers of first and second optical layers, wherein the first and second
optical layers have refractive indices along at least one axis that
differ by at least 0.04; and a protective layer disposed on an outer
surface of the multilayer optical film, the protective layer having a
thickness of less than about 0.5 um and comprising crosslinked
hydroxylated polymer.

[0006]These and other aspects of the invention are described in the
detailed description below. In no event should the above summary be
construed as a limitation on the claimed subject matter which is defined
solely by the claims as set forth herein.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007]The invention may be more completely understood in consideration of
the following detailed description in connection with the following
figures:

[0009]Disclosed herein is a protective layer which may be formed on a
multilayer optical film. The protective layer may provide numerous
advantages. For one, the protective layer can be used to prevent
imprinting caused by prism structures of prismatic films when in contact
with the multilayer optical film.

[0010]The protective layer may also be advantageous because it has a
thickness of less than about 0.5 um. Most layers capable of preventing
imprinting are 0.8 um or greater.

[0011]The protective layer may also be advantageous because it can be
applied before the multilayer polymer film is stretched to form the
multilayer optical film, and also, it can be applied during the
manufacture of the multilayer optical film. These features help to
streamline the manufacturing process by reducing the need to handle the
film which, in turn, results in fewer film defects and increases yield.

[0012]A common method of creating a protective layer is through coating a
stretched film with a solvent-based acrylate followed by drying and UV
curing. This process tends to impart tensions on one side of the
multilayer film which results in curl of the final product. The method
enabled by this invention of applying the protective coating before
stretching allows the tensions to relax which results in a dramatic
reduction in curl.

[0013]The protective layer may also be advantageous because it is formed
from an aqueous-based composition as opposed to a solvent-based
composition. It may also improve the scratch resistance of the film and
eliminate the need for protective premask films.

[0014]FIG. 1 shows a cross sectional view of an exemplary optical article
disclosed herein. Optical article 10 comprises multilayer optical film 12
comprising a plurality of alternating layers of first and second optical
layers, 14 and 16, respectively. Protective layer 18 is formed on an
outer surface of the multilayer optical film. The protective layer can
have any suitable thickness provided it can impart the desired optical
properties to the article. Generally, a thickness of less than about 0.5
um is useful. In some embodiments, the protective layer has a thickness
of less than about 0.3 um, less than about 0.1 um, or less than about
0.70 um. The protective layer is desirably thin enough so that it does
not affect the optical properties of the optical article. The protective
layer should also be thick enough to prevent imprinting of
microstructures as described below.

[0015]The protective layer comprises crosslinked hydroxylated polymer
selected from the group consisting of poly(vinyl alcohol) and a vinyl
alcohol copolymer. In general, the poly(vinyl alcohol) has properties
such as clarity and solubility in water.

[0016]In some embodiments, poly(vinyl alcohol) having a degree of
hydrolysis of from 88 to 98% may be used. Below 88% hydrolysis, imprint
resistance may be reduced, while above 98% hydrolysis the solution
viscosities may be so high as to reduce coatability of the solutions. For
example, the poly(vinyl alcohol) may have a degree of hydrolysis of from
88 to 95%. In some embodiments, poly(vinyl alcohol) having a 4% solution
viscosity of from 4 to 56 cP may be used. Solutions with viscosities in
this range are suitable for application to the film by commonly-used
industrial coating techniques. For example, the poly(vinyl alcohol) may
have a 4% solution viscosity of from 18 to 40 cP.

[0017]In some embodiments, a vinyl alcohol copolymer may be used in
combination with the crosslinking agent discussed below. Such materials
are exemplified by copolymers of ethylene and vinyl alcohol such as
EXCEVAL from Kuraray Corp, copolymers of vinyl alcohol with vinylsilanes
such as vinyltrimethoxysilane and vinyl triethoxysilane, and copolymers
of vinyl alcohol with vinylamine.

[0018]In general, the crosslinking agent may be selected such that it
allows for clear coatings with low haze (generally under 5%) and gives
good adhesion to the underlying substrate as measured by a tape pull
test, in addition to water resistance. Factors that may determine the
particular choice of crosslinker include pot life, solution stability,
and tenterability (do not want a brittle film). For example, the
crosslinking agent may comprise a dialdehyde such as glutaraldehyde or
glyoxal, an epoxy such as bisphenol A diepoxide, an isocyanate such as
XR-5305 available from Stahl Chemical, a zirconium carboxylate complex
such as Bacote 20 available from MelChemicals, an epichlorohydrin/amine
adduct such as Polycup 172 available from Hercules, a
melamine/formaldehyde resin such as Cymel 327 available from Cytec
Industries, a poly(carbodiimide) such as XR-5577 available from Stahl
Chemical, or a chemically compatible combination thereof. Other examples
of crosslinking agents include boric acid and borates, germaniac acids
and germanates, titanium salts and esters, chromates and vanadates,
cupric salts and other Group IB salts, and monoaldehydes such as
formaldehyde.

[0019]In general, the amount of crosslinking agent used depends on the
desired performance of the final coating. If too much crosslinking agent
is used, then imprint resistance is diminished. If too little is used,
then adhesion of the coating to the substrate is poor. For example, ratio
of poly(vinyl alcohol) to crosslinking agent can be from about 20:1 to
about 5:1, from about 15:1 to about 7:1, or from about 12:1 to about 9:1.

[0020]Other components that may be used in the protective layer
composition include biocides for increasing pot life. Plasticizers may
also be used for improving tenterability as the Tg and the melting
temperatures of the coated film are reduced. Examples of plasticizers
include glycerin, diethylene glycol, polyethylene glycol, and
polypropylene glycol.

[0021]The protective layer may contain other types of additives.
Preferably, such materials should be compatible with the primary
components of the coating and coating formulation, and should not
adversely affect performance attributes of the optical article. These
include coating aids such as surfactants, and coalescing solvents
including glycols, polyglycols, and substituted derivatives thereof such
as Dowanol solvents available from Dow Chemical; defoaming agents;
particulates used as, for instance, slip agents; antioxidants; catalysts
such as acids, bases, ammonium halide and sulfonate salts, sulfonium and
iodonium salts, and metal compounds such as dibutyltin esters; and pH
control agents such as buffers or trialkylamines. Use of relatively
volatile trialkylamines such as triethylamine and dimethylethanolamine as
pH stabilizers is particularly preferred for coating formulations
comprising melamine-formaldehyde crosslinking agents, since pH drift into
the acid range can cause undesirable shortened pot life and premature
gelation.

[0022]Also disclosed herein is a method of making the optical article. The
method comprises coating the protective layer composition described above
onto a multilayer optical film, thereby forming a coated multilayer
optical film. Typically, the components in the protective layer
composition are dissolved, dispersed, or suspended in a suitable solvent
for the coating step. The particular solvent used depends upon the
particular components, the desired concentrations of the components, the
desired thickness and nature of the layer, the coating method employed,
etc. Suitable solvents include water. Generally, compositions used to
form the protective layer comprise up to about 15 wt. % solids relative
to the weight of the total composition.

[0024]The protective layer composition can be cured using heat or UV
radiation or any other suitable curing technique. One preferred method of
curing is thermal activation and crosslinking of the protective layer
composition using the latent heat of a film tentering process.

[0025]The multilayer optical film may comprise any of a variety of
materials including polyesters such as polyethylene terephthalate,
polyethylene naphthalate, copolyesters or polyester blends based on
naphthalene dicarboxylic acids; polycarbonates; polystyrenes;
styrene-acrylonitriles; cellulose acetates; polyether sulfones;
poly(meth)acrylates such as polymethylmethacrylate; polyurethanes;
polyvinyl chloride; polycyclo-olefins; polyimides; glass; paper; or
combinations or blends thereof. Particular examples include polyethylene
terephthalate, polymethyl methacrylate, polyvinyl chloride, and cellulose
triacetate. Preferable examples include polyethylene terephthalate,
polyethylene naphthalate, cellulose triacetate, polypropylene, polyester,
polycarbonate, polymethylmethacrylate, polyimide, polyamide, or a blend
thereof. Preferably, the multilayer optical film is sufficiently
resistant to temperature and aging such that performance of the optical
article is not compromised over time. The thickness of the multilayer
optical film is typically less than about 2.5 mm. The multilayer optical
film may also be an orientable film such as a cast web substrate that is
coated before orientation in a tentering operation.

[0026]The multilayer optical film may comprise a light transmissive
substrate such that the optical article is suitable for use in optical
applications. Useful light transmissive multilayer optical films are
optically clear and designed to control the flow of light and may have a
transmission of greater than about 90%. The multilayer optical film may
exhibit minimal haze, having a haze value of less than about 5%, for
example, less than 2%, or less than 1%. Properties to consider when
selecting a suitable multilayer optical film include mechanical
properties such as flexibility, dimensional stability,
self-supportability, and impact resistance. For example, the multilayer
optical film may need to be structurally strong enough so that the
optical article can be assembled as part of a display device.

[0027]The multilayer optical film may comprise an optical film that is
used in a wide variety of applications such as graphic arts and optical
applications. A useful optical film may be described as a reflective
film, a polarizer film, a reflective polarizer film, a diffuse blend
reflective polarizer film, a diffuser film, a brightness enhancing film,
a turning film, a mirror film, or a combination thereof. The optical film
may comprise a multilayer optical film having ten or less layers,
hundreds, or even thousands of layers, the layers being composed of some
combination of all birefringent optical layers, some birefringent optical
layers, or all isotropic optical layers. In one embodiment, the
multilayer optical film has alternating layers of first and second
optical layers, wherein the first and second optical layers have
refractive indices along at least one axis that differ by at least 0.04.
Multilayer optical films having refractive index mismatches are described
in the references cited below.

[0029]After the protective layer is formed on a suitable multilayer
optical film, the coated multilayer optical film can then be tentered or
stretched in one or two dimensions in order to orient the multilayer
optical film. The process of orienting film, particularly polyester
films, is described in Volume 12 of The Encyclopedia of Polymer Science
and Engineering, 2nd edition, pages 193 to 216. A typical process for
fabricating biaxially oriented polyester films comprises four main steps:
(1) melt extrusion of the polyester resin and quenching it to form a web,
(2) drawing the web in the longitudinal or machine direction, (3)
subsequently or simultaneously drawing the web in the transverse
direction to create a film, and (4) heat setting the film. If biaxial
orientation is desired, the protective layer composition may be coated on
the multilayer optical film after it has been drawn in the machine
direction but before it has been subsequently drawn in the transverse
direction. Further discussion on the orientation of polymeric films can
be found in WO 2006/130142 (Karg et al.) and the previously cited
references on optical films.

[0030]The optical article may further comprise a microstructured layer
disposed on an outer surface of the multilayer optical film opposite the
protective layer, wherein the microstructured layer comprises a
structured surface having a plurality of microstructures, and the
structured surface comprises an outer surface of the optical article.
FIG. 2 shows a schematic cross-section of such an exemplary optical
article 20 having microstructured layer 22 disposed on multilayer optical
film 12. The microstructured layer has microstructured surface 24 which
comprises an array of prisms for directing light. A comprehensive
discussion of the behavior of light in a BEF film may be found, for
example, in US 2007/0115407 A1.

[0031]In general, the microstructured surface may comprise any type of
shape, pattern, etc. that may be useful in optical applications. The
microstructured surface may also comprise, for example, a series of
shapes including ridges, posts, pyramids, hemispheres and cones, and/or
they may be protrusions or depressions having flat, pointed, truncated,
or rounded parts, any of which may have angled or perpendicular sides
relative to the plane of the surface. Any lenticular microstructure may
be useful, for example, the microstructured surface may comprise cube
corner elements, each having three mutually substantially perpendicular
optical faces that typically intersect at a single reference point, or
apex. The microstructured surface may have a regularly repeating pattern,
be random, or a combination thereof. In general, the microstructured
surface comprises one or more features, each feature having at least two
lateral dimensions (i.e. dimensions in the plane of the film) less than 2
mm.

[0032]The microstructured layer may be prepared using a polymerizable
composition, a master having a negative microstructured molding surface,
and a preformed second polymeric layer sometimes referred to as a base
layer. The polymerizable composition is deposited between the master and
the second polymeric layer, either one of which is flexible, and a bead
of the composition is moved so that the composition fills the
microstructures of the master. The polymerizable composition is
polymerized to form the layer and is then separated from the master. The
master can be metallic, such as nickel, nickel-plated copper or brass, or
can be a thermoplastic material that is stable under the polymerizing
conditions and that preferably has a surface energy that permits clean
removal of the polymerized layer from the master. The first polymeric
layer with the microstructured surface may have a thickness of from about
10 to about 200 um.

[0033]The polymerizable composition may comprise monomers including mono-,
di-, or higher functional monomers, and/or oligomers, and preferably,
those having a high index of refraction, for example, greater than about
1.4 or greater than about 1.5. The monomers and/or oligomers may be
polymerizable using UV radiation. Suitable materials include
(meth)acrylates, halogenated derivatives, telechelic derivatives, and the
like, for example, those described in U.S. Pat. Nos. 4,568,445;
4,721,377; 4,812,032; 5,424,339; and 6,355,754; all incorporated herein
by reference. A preferable polymerizable composition is described in U.S.
2005/147838 A1. This polymerizable composition comprises a first monomer
comprising a major portion of 2-propenoic acid,
(1-methylethylidene)bis[(2,6-dibromo-4,1-phenylene)oxy(2-hydroxy-3,1-prop-
anediyl)]ester; pentaerythritol tri(meth)acrylate; and
phenoxyethyl(meth)acrylate.

[0034]The microstructured layer may be prepared using a polymerizable
composition, a master having a negative microstructured molding surface,
and the optical article. The polymerizable composition can be deposited
between the master and the optical layer of the optical article, and a
bead of the composition moved so that the composition fills the
microstructures of the master. The polymerizable composition is
polymerized to form the layer and is then separated from the master. The
master can be metallic, such as nickel, nickel-plated copper or brass, or
can be a thermoplastic material that is stable under the polymerizing
conditions and that preferably has a surface energy that permits clean
removal of the polymerized layer from the master. The master is further
described in U.S. Pat. No. 4,542,449; U.S. Pat. No. 5,771,328; and U.S.
Pat. No. 6,354,709. Alternatively, a pre-formed microstructured layer may
be prepared and laminated to the optical article such that the optical
layer is disposed between the microstructured layer and the substrate.

[0035]The article may be used in a graphic arts application, for example,
in backlit signs, billboards, and the like. The article may also be used
in a display device comprising, at the very least, one or more light
sources and a display panel. The display panel may be of any type capable
of producing images, graphics, text, etc., and may be mono- or
polychromatic, or transmissive or reflective. Examples include a liquid
crystal display panel, a plasma display panel, or a touch screen. The
light sources may comprise fluorescent lamps, phosphorescent lights,
light emitting diodes, or combinations thereof. Examples of display
devices include televisions, monitors, laptop computers, and handheld
devices such as cell phones, PDA's, calculators, and the like.

[0036]The invention may be more completely understood in consideration of
the following examples.

EXAMPLES

Materials

[0037]Commercially available materials are described in Table 1 and were
used as received.

[0038]A polyester multilayer optical film was prepared using methods and
materials described in US 2001/0013668 (Neavin et al.).

[0039]A UV-curable composition was used to make an outer layer having
prismatic structures. This composition is described in US 2006/0004166
(Olson et al.) and was prepared by combining a first monomer comprising a
major portion of 2-propenoic acid,
(1-methylethylidene)bis[(2,6-dibromo-4,1-phenylene)oxy(2-hydroxy-3,1-prop-
anediyl)]ester; pentaerythritol triacrylate; and phenoxyethyl acrylate.
The resin also contained 0.35 wt % DAROCUR 1173 and 0.1 wt % DAROCUR TPO
(diphenyl (2,4,6-trimethylbenzoyl)phosphine) both from Ciba Specialty
Chemicals Corp., as photoinitiators.

Test Methods

[0040]Coating samples were rated for anti-imprint performance using the
following procedure. A construction was made by pressing a 3.81
cm×4.445 cm (1.5 in×1.75 in) sample of coated multilayer
optical film against a sample of standard BEF prismatic film (from 3M®
Company) under a 50 g weight in an oven at 85° C. for 24 hr. The
resulting coated multilayer optical film was then rated on a 0 to 9
scale, where 0 represents no visible imprinting.

[0041]Haze was measured using a Byk-Gardner HazeGard Plus meter. Adhesion
of the crosslinked poly(vinyl alcohol layer) to the multilayer optical
film was determined by staining the coating with a few drops of an
aqueous solution of 1 g iodine and 15.82 g potassium iodide in 328 g
deionized water, allowing it to dry, and running a tape pull test after
lamination with a piece of 3M® 610 adhesive tape available from 3M®
Company. Tests were run on the edge and center of the coated area.
Coatings were rated "Pass" or "Fail" depending on whether any of the
coating was removed with the tape. Visualization of the removed
protective coating can be enhanced by treating the sample with a few
drops of an aqueous solution of 1 g iodine and 15.82 g potassium iodide
in 328 g deionized water. Abrasion susceptibility of the PVA coatings was
measured using 5 cycles on a Taber abrader equipped with a CS-11 wheel,
and results are reported as ΔHaze=Haze (after abrasion)-Haze
(initial).

Examples 1-15

[0042]PVA-based coating formulations shown in Table 2 were prepared in
deionized water, and all formulations included 0.1 wt % TOMADOL 25-9 to
ensure uniform wetting of the substrate. The formulations were coated
inline at 10.2 m/min (33.6 ft/min) on a freshly extruded multilayer
optical film substrate using a #6 wire-wound rod. Coatings were applied
just prior to the film entering a drying oven set at 54° C. The
other side of the web was continuously primed with a coating of 6 wt. %
RHOPLEX dispersion in deionized water also containing 1.5 wt % CYMEL 327
crosslinker, 0.25 wt % C4045 catalyst, and 0.1 wt % TOMADOL 25-9, applied
by air knife (applicator roll speed 40 ft/min, backup roll gap 50 mil,
air pressure 2 psig). Immediately after coating, the film passed into a
tenter that was divided into three zones--preheat, stretch, and heat set.
Temperatures in deg C and dwell times in sec, respectively, for the three
zones were as follows: Preheat, 122, 29; Stretch, 113, 57; Heat Set, 190,
25. Tranverse draw ratio in the stretch zone was 7.96:1, yielding a final
substrate thickness of 3.66 mil.

[0043]Samples of each coating after tentering and winding were evaluated
for haze and clarity, determination of coating adhesion, and abrasion
using the methods described above with results shown in Table 3. A
microstructured layer was then applied to the RHOPLEX-primed side with
the UV-curable composition, which were prepared into brightness enhancing
films as described in Olson et al. A master tool having 90° apex
angles as defined by the slope of the sides of the prisms was used. The
mean distance between adjacent apices was about 24 um. Processing
conditions included line speed 60 ft/min; resin temperature 71°
C.; tool temperature 60° C.; lamps, two D bulbs operating at 100%
power on the tool, with one post-cure D bulb at 85% power; oven
temperature 68° C. The resulting laminates were used to measure
the anti-imprint performance of the PVA coating as described above.
Results from these experiments are shown in Table 3 below.

Comparative Example 1

[0044]Comparative Example 1 consisted of the multilayer optical film
having a hardcoat of about 0.8 um. The hardcoat was obtained by coating a
UV-curable, isopropanol-based formulation of acrylated silica particles,
N,N-dimethyl acrylamide, and pentaerythritol triacrylate monomers.
Preparation of the coating formulation, including coating and curing
conditions, are described in Example 3 of U.S. Pat. No. 6,299,799 B1
(Craig et al.). Haze, anti-imprint, and abrasion testing were carried out
as described above.

Comparative Example 2

[0045]Comparative Example 1 consisted of the multilayer optical film.
Haze, anti-imprint, and abrasion testing were carried out as described
above.